1. Technical Field
This invention relates to the deposition of metal onto a surface using a spraying process. The invention is especially useful in spraying onto internal cylindrical surfaces, and a typical example of such a surface is the internal surface of an internal combustion engine cylinder. The invention is however equally applicable to other cylindrical bores and to other surfaces.
2. Description of the Prior Art
Both plasma spray and arc spray processes are known for depositing metal onto a surface. The plasma spray process uses a powder feed, whereas in the arc spray process the material to be deposited is supplied in the form of wire. Plasma deposition has the advantage of a hot, short flame giving high molten particle velocities and dense deposits but arc spray equipment has the advantages that it is cheaper than plasma and that the rate of deposition is higher.
For use in the coating of cylindrical surfaces, arc spray would be the method of choice, but there are formidable difficulties in designing a rotating twin-wire spray gun for cylindrical surfaces because of the need to rotate two heavy spools of feed wire each occupying a large amount of space. This is particularly complicated when the cylinder bores of a combustion engine are to be coated, because in this application it is desirable to be able to simultaneously coat a number of adjacent, parallel, cylindrical bores.